Thermoplastic vulcanizates (“TPV”) are vulcanized compositions that include finely dispersed crosslinked elastomer particles in a continuous thermoplastic phase. TPVs can be produced by a process called dynamic vulcanization, where the elastomeric component is selectively crosslinked during melt mixing with molten thermoplastics. TPVs have the benefits of the elastomeric properties provided by the elastomer phase and processability provided by the thermoplastic phase. TPVs can be used in the manufacture of a variety of products, and may be useful for making automotive interiors, such as instrument panels, floor consoles, and door panels.
Mineral oil, free process oil, and/or extender oils are usually contained in compositions for making TPVs. The different types of oil and the process of adding the oil can affect the properties of the TPV. For example, when TPVs are used in automotive interior applications, certain substances in the process oils can evaporate at elevated temperatures and can cause fogging on the glass or other surfaces within the automobile. Attempts to reduce fogging have been made by using high viscosity process oils and/or solid resins to produce TPVs. However, such processes add additional process complexity in the need to handle multiple oils, and the use of high viscosity oil may also undesirably increase the viscosity of the TPV.
EP Patent Application Publication No. 0776937 A2 discloses thermoplastic elastomer compositions that are prepared using hydrosilylation crosslinking, where the hydrosilylation is carried out in the presence of a process oil which is substantially free of materials having a chemical behavior of a Lewis base.
U.S. Pat. No. 6,399,709 discloses a process for producing a thermoplastic elastomer composition, which comprises the step of feeding rubber and a thermoplastic resin through independent feed throats to an extruder to perform melt kneading. The thermoplastic elastomer composition has a haze value of a glass plate of not higher than about 2%, provided that the haze value is measured with use of an apparatus according to regulations prescribed in ISO 6452 after a lapse of heating time of 20 hours at a heating temperature of 100° C.
U.S. Pat. No. 6,750,292 provides thermoplastic vulcanizates containing 5-70 parts by weight semi-crystalline polyolefin, 95-30 parts by weight rubber containing an at least partially vulcanized polymer, and oil whereby the sum of the concentration of aromatic compounds and the concentration of polar compounds in the oil are less than 4.5 wt %.
U.S. Pat. No. 6,774,162 and PCT Publication No. WO 2000/49086 provide thermoplastic vulcanizate compositions comprising (A) a thermoplastic; (B) a substantially non-cross-linked polyethylene, (C) an at least partially vulcanized rubber; and (D) a softner.
U.S. Pat. No. 7,737,221 provides a thermoplastic elastomer compositions having a Shore A hardness of less than 35 and comprising a thermoplastic polyolefin and a dynamically vulcanized elastomer having an oil/elastomer ratio of at least 2/1.
U.S. Patent Application Publication Ser. No. 2013/0046049 A1 discloses a method for producing a thermoplastic elastomer composition, the method comprising subjecting components (A), (B), (C), and (D) to dynamic thermal treatment in a melt-kneading apparatus, wherein (A) is an ethylene-alpha-olefin based copolymer rubber, (B) is a polyolefin resin, (C) is a liquid in which an alkylphenol resin has been dispersed and/or dissolved in a mineral oil, and (D) is a metal halide.
A study by T. Hilbert and G. Chitnis et al. in Premium Base Oil Production by the Hydroprocessing Route published on www.digitalrefining.com in August 2013 described the olatility of different compositions in lube base oil. As shown in FIG. 10 of the article, the volatility of a base oil increases in order from normal paraffin to isoparaffin to naphthene to aromatics to multi-ring naphthalene and to multi-ring aromatic, that is normal paraffin oils are the least volatile and multi-ring aromatic oils exhibit the most volatility.
While the above references have described various different TPV compositions and methods for making the same, there is still a need for TPV compositions with improved fogging properties. Thus, it would be desirable to provide TPVs that exhibit improved fogging properties without exhibiting any significant deterioration in other desired physical and mechanical properties.